As a method for measuring the brain function of a baby, there is disclosed a method for measuring brain waves generated from the brain stem in response to stimulation sounds. This method can mainly measure the response of the brain stem and is difficult to measure the high-order functions controlled by the cerebral cortex.
As a method with light, a method for measuring the activities of the cerebral cortex is proposed. In biological measurement with light, an instrument measuring the biological functions with visible to near infrared light is disclosed in Japanese Patent Application Laid-Open No. 57-115232 or Japanese Patent Application Laid-Open No. 63-275323. Further, a proposal about a brain function image measurement technique by application of this measurement principle (optical topography) is disclosed in Japanese Patent Application Laid-Open No. 9-98972.
These use light guide means, typically, an optical fiber, illuminate biological tissue, and collect and measure the light scattered in biological tissue in the positions several mm to several cm away (hereinafter, abbreviated as the scattering light in biological tissue). Based on the intensity of the measured scattering light in biological tissue, the concentration of absorber in biological tissue, typically, oxygenated Hemoglobin and deoxygenated Hemoglobin, or a value corresponding to the concentration, is obtained. When obtaining the concentration of absorber or the value corresponding to the concentration, the absorption characteristic of targeted absorber corresponding to the wavelength of the illuminating light is used. Typically, when measuring a biological deep part, light which has a wavelength within the range of 650 to 1300 nm and is high in biological permeability, is used.
Such method with light is typically used for biological measurement of a human, in particular, an adult.
The method with light can also measure a baby in view of safety and may measure the high-order brain functions of the baby.
It has been, however, difficult to simultaneously measure the brain stem and the high-order functions accompanying the activities of the cerebral cortex of a baby. If this problem is solved, the low-order to high-order brain functional disorders will be able to be found at an early stage in babyhood. The low-order to high-order brain functional disorders (for example, auditory, language and visual disorders) are often found at the age of two or three and starting speaking. In such case, language acquirement is delayed than normal, thereby requiring tremendous labor for recovering the delay.
A social demand is significant in development of a technical method or an instrument capable of measuring the main brain functional disorders (of the visual, auditory and language functions) at an early stage.
For that purpose, the following two major technical problems (1) and (2) must be solved.
(1) A method for fixing an optical fiber used for the measurement of biological tissue with light
The measurement of biological tissue with light has means for illumination with light (hereinafter, abbreviated as illuminating means) and means for collecting light transmitted through biological tissue (hereinafter, abbreviated as light collecting means). As the illuminating means and the light collecting means, an optical waveguide, typically, an optical fiber or an optical fiber bundle, is often used. A set of optical waveguides for illumination and light collection is a minimum unit indicating one measurement position (hereinafter, abbreviated as an illumination and light collection pair).
An instrument performing biological image measurement by setting a plurality of the minimum units is proposed in Japanese Patent Application Laid-Open No. 9-98972. The distance between the illumination position and the light collection position of the illumination and light collection pair (hereinafter, abbreviated as the distance between the illumination and light collection pair) is changed by the size or depth of an area to be measured. The proposal of Japanese Patent Application Laid-Open No. 9-98972 discloses an arrangement form in which an optical waveguide for illumination and an optical waveguide for light collection are arranged alternately on the tops of a square grid so that the distances between the illumination and light collection pairs are equally spaced. Using the arrangement form, one optical waveguide is shared among a plurality of illumination and light collection pairs so as to make image measurement by a small number of optical waveguides. The optical waveguides can be worn on biological tissue in a short time.
The arrangement form can be easily applied to a small area of biological tissue so as to be approximated on the plane of the biological tissue (for example, about 15 cm square for the head), but is difficult to apply to an area having a large curvature. In particular, the head shape of a newborn or a baby has a large curvature so that the difference among individuals is large. When measuring a newborn or a baby, it is impossible for the subject to wait quietly. There arises the problem that the deviation of a probe due to movement must be suppressed, which cannot be expected in an adult.
Means for measuring the brain functions of a newborn or a baby has been limited to an electroencephalogram. The spatial resolution of the electroencephalogram is not very high, making it difficult to separate information on the brain stem as the center part of the brain and the cerebral cortex of the brain surface. On the contrary, a brain function measurement method based on the measurement with light enables non-invasive measurement of the cerebral cortex related strongly to the high-order brain functions particularly developed in a human. It is expected as a very effective method for recognizing the development process of the high-order functions. Although it is known to be effective in principle, a biological measurement probe fixing waveguides for illumination and light collection has not been developed.